Oxynitride phosphor activated by a rare earth element, and sialon type phosphor

ABSTRACT

An oxynitride phosphor activated by a rare earth element, represented by the formula Me x Si 12−(m+n) Al (m+n) O n N 16−n :Re1 y Re2 x , wherein a part or all of metal Me (where Me is at least one metal selected from the group consisting of Ca, Mg, Y and lanthanide metals excluding La and Ce) in α-sialon solid solution, is substituted by lanthanide metal Re1 (where Re1 is at least one metal selected from the group consisting of Ce, Pr, Eu, Tb, Yb and Er), or two lanthanide metals Re1 and a coactivator Re2 (where Re2 is Dy), to be an emission center.  
     A sialon type phosphor in the form of a powder comprising at least 40 wt % of α-sialon represented by the formula (Ca x ,M y ) (Si, Al) 12 (O, N) 16  (where M is at least one metal selected from the group consisting of Eu, Tb, Yb and Er, 0.05&lt;(x+y)&lt;0.3, 0.02&lt;x&lt;0.27 and 0.03&lt;y&lt;0.3) and having a structure such that Ca sites of Ca-α-sialon are partially substituted by other metal M, at most 40 wt % of β-sialon, and at most 30 wt % of unreacted silicon nitride.

[0001] The present invention relates to an oxynitride phosphor activatedby a rare earth element, which makes high luminance of a white lightemitting diode (white LED) employing a blue light emitting diode (blueLED) as a light source possible. Further, the present invention relatesto a sialon type phosphor optically activated by a rare earth element,which makes high luminance of white LED employing blue LED or anultraviolet emitting diode (ultraviolet LED) as a light source possible.

[0002] Phosphors are widely known wherein a silicate, a phosphate (suchas apatite) or an aluminate is used as a matrix material and such amatrix material is activated by a transition metal or a rare earthmetal. On the other hand, phosphors wherein a nitride or an oxynitrideis used as a matrix material and such a matrix material is activated bya transition metal or a rare earth metal, are not well known.

[0003] With respect to nitride phosphors, for example, German Patent789,890 discloses aluminum nitride activated by manganese, and aliterature “Izv. Akad. Nauk SSSR, Neorg. Master” 17(8), 1431-5 (1981)discloses magnesium silicon nitride (MgSiN₂) activated by a rare earthelement. Recently, only a red-emitting phosphor having ZnSiN₂ having adistorted wurtzite structure activated by Mn (T. Endo et al. “Highpressure synthesis of “periodic compound” and its optical and electricalproperties”, In T. Tsumura, M. Doyama and Seno (Editors), NewFunctionality Materials, Volume C, Elsevier, Amsterdam, The Netherlands,pp. 107-112 (1993)), a red-emitting phosphor having CaSiN₂ activated byEu (S. S. Lee et al. “Photoluminescence and ElectroluminescenceCharacteristic of CaSiN₂:Eu”, Proc. SPIE-Int. Soc. Opt. Eng., 3241,75-83 (1997)) and a phosphor having Ba₂Si₅N₈ activated by Eu, have beenreported.

[0004] With respect to oxynitride phosphors, a phosphor using β-sialonas the matrix material (JP-A-60-206889), a phosphor having a silicatemineral or a Y—Si—O—N type composite silicon oxynitride having anapatite structure activated by Ce (J. W. H. van Krevel et al. “Longwavelength Ce³⁺ emission in Y—Si—O—N materials”, J. Alloys andCompounds, 268, 272-277 (1998)), a Ba_(1−x)Eu_(x)Al₁₁O1₆N phosphorhaving a β-alumina structure (H. Hintzen et al. “On the Existence ofEuropium Aluminum Oxynitrides with a Magnetoplumbite or β-Alumina-TypeStructure”, J. Solid State Chem., 142, 48-50 (1999), and S. R. Jansen etal. “Eu-Doped Barium Aluminum Oxynitride with β-Alumina-Type Structureas New Blue-Emitting Phosphor”, J. Electrochem. Soc., 146, 800-806(1999)) have been reported. Recently, only a phosphor using anoxynitride glass as a matrix material, has been proposed(JP-A-2001-214162).

[0005] Whereas, white LED has been used, for example, in the field wherereliability is required for e.g. emergency illumination or signal light,in the field where miniaturization and weight reduction are desired, forexample, for in-vehicle lightening or liquid crystal backlight, or inthe field where visibility is required for e.g. guide plates at railwaystations. The emitted color of such white LED, i.e. white light, isobtained by color mixing of lights and is one obtained by mixing of bluelight emitted by blue LED of InGaN type with a wavelength of from 450 to550 nm as a light source and yellow light emitted from the phosphor.

[0006] As a phosphor suitable for such white LED, a phosphor having Cedoped to a YAG type oxide represented by the composition formula (Y,Gd)₃ (Al, Ga)₅O₁₂, is most commonly employed. This phosphor is appliedas a thin coating on the surface of the above-mentioned InGaN type blueLED as a light source.

[0007] However, an oxide type phosphor usually has a drawback that theemission intensity substantially decreases if the excitation wavelengthexceeds 400 nm. Accordingly, white LED obtained by coating the surfaceof a blue LED chip with a phosphor made of a YAG type oxide, has beenconsidered to have a difficulty such that the excitation energy of theYAG type oxide as the phosphor does not agree to the excitation energyof the blue LED as the light source, whereby the excitation energy cannot efficiently be converted, and it is difficult to prepare white LEDhaving high luminance.

[0008] In a first aspect, the present invention has been made in view ofthe above circumstances, and it is an object of the present invention toprovide an oxynitride phosphor activated by a rare earth element, whichmakes high luminance of a white light emitting diode (white LED)employing a blue light emitting diode (blue LED) as a light sourcepossible.

[0009] The inventors of the present invention have found that thepositions of excitation/emission peaks shown by a conventional oxidetype phosphor shift towards a long wavelength side, when oxygen atomssurrounding the rare earth element as the emission center aresubstituted by nitrogen atoms to reduce the influence which electrons ofthe rare earth element receive from the surrounding atoms, and on thebasis of this technical finding, they have proposed a phosphor whichemploys an oxynitride glass as the matrix material and which has anexcitation spectrum extending to a visible region (≦500 μm).

[0010] On the basis of the above technical finding, the presentinventors have further studied the presence of another oxynitridephosphor and as a result, have found that a crystalline oxynitridephosphor employing α-sialon having a higher nitrogen content than theoxynitride glass, as the matrix material, wherein a part or all of metalMe (where Me is at least one metal selected from the group consisting ofCa, Mg, Y and lanthanide metals excluding La and Ce) in α-sialon solidsolution as the matrix material, is substituted by lanthanide metal Re1(Re1 is at least one metal selected from the group consisting of Ce, Pr,Eu, Tb, Yb and Eu), or two lanthanide metals Re1 and a coactivator Re2(where Re2 is Dy), to be an emission center, makes high luminance whiteLED possible. Thus, the first aspect of the present invention has beenaccomplished on the basis of this discovery.

[0011] Thus, according to the first aspect, the present inventionprovides:

[0012] 1. An oxynitride phosphor activated by a rare earth element,represented by the formula Me_(x)Si_(12−(m+n)) ^(Al)_((m+n))O_(n)N_(16−n):Re1_(y)Re2_(x), wherein a part or all of metal Me(where Me is at least one metal selected from the group consisting ofCa, Mg, Y and lanthanide metals excluding La and Ce) in α-sialon solidsolution, is substituted by lanthanide metal Re1 (where Re1 is at leastone metal selected from the group consisting of Ce, Pr, Eu, Tb, Yb andEr), or two lanthanide metals Re1 and a coactivator Re2 (where Re2 isDy), to be an emission center.

[0013] 2. The oxynitride phosphor activated by a rare earth elementaccording to Item 1, wherein when metal Me is bivalent, 0.6<m<3.0 and0≦n<1.5.

[0014] 3. The oxynitride phosphor activated by a rare earth elementaccording to Item 1, wherein when metal Me is trivalent, 0.9<m<4.5 and0<n≦1.5.

[0015] 4. The oxynitride phosphor activated by a rare earth elementaccording to any one of Items 1 to 3, wherein m=1.5, n=0.75 and in thecomposition formula Me_(x)Si_(9.75)Al_(2.25)O_(0.75)N_(15.25):Re1_(y)^(Re)2_(z), 0.3<x+y<0.75 and 0.01<y+z<0.7 (where y>0.01 and 0.0≦z<0.1).

[0016] 5. The oxynitride phosphor activated by a rare earth elementaccording to Item 4, wherein 0.3<x+y+z<1.5, 0.01<y<0.7 and 0≦z<0.1.

[0017] 6. The oxynitride phosphor activated by a rare earth elementaccording to Item 2, 4 or 5, wherein metal Me is Ca.

[0018] The above oxynitride phosphor is composed of a single phase ofα-sialon, whereby it is required to incorporate a large amount of therare earth metal, which limits reduction of costs.

[0019] In a second aspect, the present invention has been made undersuch circumstances, and it is another object of the present invention toprovide a sialon type phosphor comprising α-sialon dissolving a rareearth element in the structure, β-sialon and unreacted silicon nitride,which makes high luminance of a white light emitting diode (white LED)employing a blue light emitting diode (blue LED) as a light sourcepossible.

[0020] Thus, in the second aspect, the present invention provides:

[0021] 7. A sialon type phosphor in the form of a powder comprising atleast 40 wt % of α-sialon represented by the formula (Ca_(x), My) (Si,Al)₁₂ (O, N)₁₆ (where M is at least one metal selected from the groupconsisting of Eu, Tb, Yb and Er, 0.05<(x+y)<0.3, 0.02<x<0.27 and0.03<y<0.3) and having a structure such that Ca sites of Ca-α-sialon arepartially substituted by other metal M, at most 40 wt % of β-sialon, andat most 30 wt % of unreacted silicon nitride.

[0022] 8. The sialon type phosphor according to Item 7, wherein thechemical composition of the powder as a whole, is within a range definedby three compositional lines of Si₃N₄−a(M₂O₃˜9AlN), Si₃N₄−b(CaO˜3AlN)and Si₃N₄−c(AlN˜Al₂O₃), where 4×10⁻³<a<4×10⁻², 8×10⁻³<b<8×10⁻² and10⁻²<c<10⁻¹.

[0023] In the accompanying drawings;

[0024]FIG. 1 is a chart showing excitation spectra relating to redemission of a Ca-α-sialon phosphor wherein the activating amount of Eu²⁺ions was changed.

[0025]FIG. 2 is a chart showing emission spectra of a Ca-α-sialonphosphor wherein the activating amount of Eu²⁺ ions was changed.

[0026]FIG. 3(a) is a chart showing an excitation spectrum of aCa-α-sialon phosphor activated by Pr³⁺ ions.

[0027]FIG. 3(b) is a chart showing an emission spectrum of a Ca-α-sialonphosphor activated by Pr³⁺ ions.

[0028]FIG. 4(a) is a chart showing an excitation spectrum of aCa-α-sialon phosphor activated by Tb³⁺ ions.

[0029]FIG. 4(b) is a chart showing an emission spectrum of a Ca-α-sialonphosphor activated by Tb³⁺ ions.

[0030]FIG. 5(a) is a chart showing an excitation spectrum of aCa-α-sialon phosphor activated by both Eu²⁺ ions and Dy³⁺ ions.

[0031]FIG. 5(b) is a chart showing an emission spectrum of a Ca-α-sialonphosphor activated by both Eu²⁺ ions and Dy³⁺ ions.

[0032]FIG. 6(a) is a chart showing an excitation spectrum of aY-α-sialon phosphor activated by Eu³⁺ ions.

[0033]FIG. 6(b) is a chart showing an emission spectrum of a Y-α-sialonphosphor activated by Eu³⁺ ions.

[0034]FIG. 7 is a chart showing an excitation spectrum (a) and anemission spectrum (b) of a Yb²⁺ α-sialon phosphor.

[0035]FIG. 8 is a chart showing an excitation spectrum (a) and anemission spectrum (b) of an Eu³⁺ α-sialon phosphor.

[0036]FIG. 9 is a composition diagram showing the chemical compositionrange (the composition range between the hatched two triangles) of thephosphor according to the second aspect of the present invention and thechemical composition range of the powder as a whole.

[0037]FIG. 10 is a graph showing excitation spectra of Example 8 (solidline) and Example 9 (dotted line).

[0038]FIG. 11 is a graph showing emission spectra of Example 8 (solidline 1) and Example 9 (dotted line 2).

[0039] Now, the present invention will be described in detail withreference to the preferred embodiments.

[0040] The oxynitride phosphor activated by a rare earth elementaccording to the first aspect of the present invention, is representedby the formulaMe_(x)Si_(12−(m+n))Al_((m+n))O_(n)N_(16−n):Re1_(y)Re2_(x), wherein apart or all of metal Me (where Me is at least one metal selected fromthe group consisting of Ca, Mg, Y and lanthanide metals excluding La andCe) in α-sialon solid solution, is substituted by lanthanide metal Re1(where Re1 is at least one metal selected from the group consisting ofCe, Pr, Eu, Tb, Yb and Er), or two lanthanide metals Re1 and acoactivator Re2 (where Re2 is Dy), to be an emission center, asmentioned above.

[0041] In the oxynitride phosphor activated by a rare earth element ofthe present invention, metal Me is dissolved in an amount of from theminimum of 1 atom per 3 unit cells to the maximum of 1 atom per 1 unitcell, of α-sialon containing 4 formula of (Si, Al)₃(N, O)₄. The solidsolubility limits are usually such that when, in the above formula,metal Me is bivalent, 0.6<m<3.0 and 0≦n<1.5, and when metal Me istrivalent, 0.9<m<4.5 and 0≦n<1.5. If the composition is outside theseranges, it will not form single phase α-sialon.

[0042] The inter-ionic distance of lanthanide metal Re1 whichsubstitutes a part or all of such metal Me for activation and which willbe the emission center, is at least about 5 Å, which is far larger thanfrom 3 to 4 Å in a conventional phosphor. This is believed to be areason why it is possible to suppress the remarkable decrease of theemission intensity due to optical loss, which used to result when theconcentration of lanthanide metal as the emission center contained inthe matrix material, is high.

[0043] Further, with the oxynitride phosphor activated by a rare earthelement of the present invention, the above-mentioned metal Me can besubstituted by lanthanide metal Re2 as a coactivator in addition tolanthanide metal Re1 to be the emission center. The coactivating effectsof lanthanide metal Re2 as such a coactivator, are considered to be twofold. One is a sensitizing effect, and the other is an effect to form atrap level of a carrier anew thereby to have high persistence developedor improved, or to have thermoluminescence improved. The amount of suchlanthanide metal Re2 to be substituted is usually 0.0≦z<0.1 in the aboveformula, since it is a coactivator.

[0044] Further, the oxynitride phosphor activated by a rare earthelement of the present invention is one comprising α-sialon as thematrix material and thus is essentially different in the composition andthe crystal structure from a phosphor comprising β-sialon as the matrixmaterial.

[0045] Namely, β-sialon is represented by the formulaSi_(6−z)Al_(x)O_(z)N_(8−z) (0<z<4.2) and is a solid solution of β-typesilicon nitride, wherein a part of Si sites is substituted by Al and apart of N sites is substituted by O.

[0046] Whereas, α-sialon is represented by the formulaMe_(x)Si_(12−(m+n))Al_((m+n))O_(n)N_(16−n) and is a solid solution ofα-type silicon nitride wherein a part of Si—N bonds is substituted byAl—N bonds, and certain specific metal Me (Me is at least one metalselected from the group consisting of Ca, Mg, Y and lanthanide metalsexcluding La and Ce) is incorporated into interstitial sites to form thesolid solution.

[0047] Thus, the two are different in the solid solution state, i.e.β-sialon has a high oxygen content, and α-sialon has a high nitrogencontent.

[0048] In a phosphor prepared by adding at least one of oxides of rareearth metals such as Ce, Pr, Eu, Tb, Yb and Er which will be theemission center, to β-sialon as the matrix material, such metals are notsoluble in α-sialon, whereby it will be a mixed material wherein acompound containing such a rare earth metal is formed among β-sialonparticles.

[0049] Whereas, when α-sialon is used as the matrix material, metal Me(where Me is at least one metal selected from the group consisting ofCa, Mg, Y and lanthanide metals excluding La and Ce) is dissolved in itscrystal structure, and rare earth elements such as Ce, Pr, Eu, Tb, Yband Er which will be the emission center, will partly substitute themetal Me sites, whereby an oxynitride phosphor composed of a singlephase of an α-sialon structure, can be obtained.

[0050] Accordingly, a phosphor obtained by using β-sialon as the matrixmaterial and a phosphor obtained by using α-sialon as the matrixmaterial are totally different in the composition and the crystalstructure, and such differences are reflected to the emissioncharacteristics of the phosphors.

[0051] Namely, when β-sialon is used as the matrix material, theluminescent color of phosphors prepared by doping Er oxide to β-sialonas disclosed in Examples 33 to 35 in the above-mentioned JP-A-60-206889,is blue (410 to 440 nm). Whereas, with the oxynitride phosphor activatedby a rare earth element of the present invention, the luminescent coloractivated by the same Er is from orange to red (570 to 590 nm), as shownin FIG. 2 and Example 1 given hereinafter. From this phenomenon, it isconsidered that Er is taken into the crystal structure of α-sialon,whereby Er will receive an influence of nitrogen atoms constituting thecrystal, and elongation of the wavelength in the emission spectrum,which can hardly be realized with the phosphor using an oxide as thematrix material, can be facilitated.

[0052] Further, since the matrix material is α-sialon, the oxynitridephosphor activated by a rare earth element of the present invention,also has merits of α-sialon as the matrix material.

[0053] Namely, α-sialon is excellent in thermal and mechanicalproperties and capable of suppressing a thermal relaxation phenomenonwhich causes a loss of excitation energy. Accordingly, with theoxynitride phosphor activated by a rare earth element of the presentinvention, the degree of decrease in the emission intensity with anincrease of the temperature, will be small. Accordingly, the usefultemperature range will be broadened as compared with conventionalphosphors.

[0054] Further, α-sialon is excellent also in the chemical stability,and accordingly, it will be a phosphor excellent in light resistance.

[0055] Further, the oxynitride phosphor activated by a rare earthelement of the present invention can be made to be excited byultraviolet rays, X-rays or electron beams, by selecting the O/N ratioin the composition or the type of lanthanide metal Re1 to be substitutedfor metal Me and by the presence or absence of lanthanide metal Re2 as acoactivator.

[0056] Especially, among oxynitride phosphors activated by rare earthelements of the present invention, one wherein m=1.5, n=0.75 and in thecomposition formulaMe_(x)Si_(9.75)Al_(2.25)O_(0.75)N_(15.25):Re1_(y)Re2_(z), 0.3<x+y<0.75and 0.01<y+z<0.7 (where y>0.01 and 0.0≦z<0.1), or 0.3<x+y+z<1.5,0.01<y<0.7 and 0.0≦z<0.1, and metal Me is Ca, is particularly excellentin the emission characteristics and is expected to be applied not onlyto phosphors to be excited by ultraviolet-visible light, but also tophosphors to be excited by electron beams.

[0057] Thus, the oxynitride phosphor activated by a rare earth elementof the present invention is useful particularly for the preparation ofwhite LED and is a phosphor suitable for InGaN type blue LED as a lightsource.

[0058] Now, the second aspect of the present invention will bedescribed.

[0059] As a result of an extensive study on the compositional range forhigh emission efficiency on the basis of the above technical finding,the present invention have found a mixed material comprising α-sialonhaving a part of Ca sites of α-sialon substituted by at least one ofrare earth metals (M) (where M is Eu, Tb, Yb or Er), β-sialon andunreacted silicon nitride, and having characteristics equal to α-sialonalone, and the second aspect of the present invention which makes highluminance white LED possible has been accomplished.

[0060] In the second aspect of the present invention, a phosphor can beprepared by adding a rare earth metal in an amount smaller than theamount required for the phosphor of the first aspect of the presentinvention, which is useful for reducing the cost of the material.

[0061] Further, the matrix material is α-sialon, and the sialon typephosphor activated by the rare earth element of the second aspect of thepresent invention, also has merits of α-sialon as the matrix materialand is excellent in chemical, mechanical and thermal characteristics andstable as a phosphor material and expected to have a long useful life.Further, it is excellent in the above characteristics and is capable ofsuppressing a thermal relaxation phenomenon which causes a loss of theexcitation energy. Accordingly, with α-sialon having a rare earthelement in the solid solution together with Ca according to the secondaspect of the present invention, the degree of decrease in the emissionintensity with an increase of the temperature, will be small.Accordingly, the useful temperature range will be broadened as comparedwith conventional phosphors.

[0062] Further, the α-sialon phosphor dissolving Ca and a rare earthelement according to the second aspect of the present invention, can bemade to be excited by ultraviolet rays, X-rays or electron beams byselecting the O/N ratio in the composition formula or by selecting thetype of metal M.

[0063] Namely, in the second aspect, the present invention provides amaterial showing emission characteristics equal to the first aspect ofthe present invention even if the amount of rare earth metals (such asEu, Tb, Yb and Er) to be added, is reduced. In order to stabilize theα-sialon structure, solid solution of elements in an amount of at leasta prescribed level, is required. When the solid solution amounts of Caand a trivalent metal are represented by x and y, respectively, thevalue (x+y) is required to be at least 0.3 in a thermodynamicequilibrium state.

[0064] In the second aspect of the present invention, the phosphor ismade of a material having a composition which comprises not onlyα-sialon but also β-sialon or unreacted silicon nitride, for a reason ofeither addition in an amount smaller than the prescribed amount or notreaching the thermodynamical equilibrium.

[0065] In the chemical composition of the powder, the amounts of metalsadded in the phosphor of the present invention are within the ranges of0.05<(x+y)<0.3, 0.02<x<0.27 and 0.03<y<0.3. If the amounts added arelower then the above lower limits, the amount of α-sialon decreases,whereby the emission intensity decreases. If the amounts added exceedthe above upper limits, the material tends to be α-sialon only, and theobject of the second aspect of the present invention can not beaccomplished as the amounts added are too much. If the amounts added arewithin the ranges of the above formulae, it is possible to obtain asialon type phosphor comprising at least 40 wt % of α-sialon, at most 40wt % of β-sialon and at most 30 wt % of unreacted silicon nitride.Despite the presence of unreacted silicon nitride, the emissionintensity is high, for such a reason that α-sialon epitaxially grows onsilicon nitride, and mainly the surface portion responds to theexcitation light, whereby characteristics substantially close to singleα-sialon can be obtained.

[0066] The phosphor of the present invention can be obtained by heatinga mixed powder of Si₃N₄—M₂O₃—CaO—AlN—Al₂O₃ system in an inert gasatmosphere within a range of from 1,650 to 1,900° C. to obtain asintered product and pulverizing the sintered product. CaO is unstableand readily reacts with steam in air. Accordingly, it is common that itis added in the form of calcium carbonate or calcium hydroxide, and itwill be converted to CaO in the process of heating at a hightemperature.

[0067] If the total chemical composition of the phosphor of the secondaspect of the present invention is described by the composition rangesof M-α-sialon, Ca-α-sialon and β-sialon, it is within a range defined bythree compositional lines of Si₃N₄−(M₂O₃˜9AlN), Si₃N₄−b(CaO˜3AlN) andSi₃N₄—c(AlN˜Al₂O₃), where 4×10 ⁻³<a<4×10⁻², 8×10⁻³<b<8×10⁻² and10⁻²<c<10⁻¹.

[0068] As represented by the compositional region of a triangularpyramid having silicon nitride at the apex, the phosphor of the presentinvention falls within the composition range between the two triangles,as shown in FIG. 9. The amount of solid solution within the actuallyformed α-sialon particles is x+y<0.3 i.e. the amount required forstabilization, as mentioned above. Within a composition range where theamount added is less than this level, the product will be constituted byα-sialon having a composition of (x+y)<0.3, β-sialon dissolving no rareearth and unreacted silicon nitride. It is common that additionally asmall amount (not more than 5 wt %) of a glass phase will beco-existent.

[0069] According to the second aspect of the present invention, even ifthe amount of a rare earth added is small, and the composition is notα-sialon alone, α-sialon will form on the surface of particles, wherebythe emission characteristics are excellent, and such a product isexpected to be applicable not only to an ultraviolet-visible lightexcitation phosphor but also to an electron beam excitation phosphor.

[0070] Thus, the composite sintered product containing Ca-α-sialondissolving a rare earth simultaneously, according to the presentinvention, is effective for practical use of white LED.

[0071] Now, the present invention will be described in further detailwith reference to Examples. However, it should be understood that thepresent invention is by no means restricted to such specific Examples.

[0072] Oxynitride phosphors activated by rare earth elements werereacted for one hour in a nitrogen atmosphere of 1 atm at 1,700° C.under a pressure of 20 MPa by means of a hot press apparatus, to prepareeight types of material powders, as shown below. The molar ratios ofchemical regents used as starting materials for these materials are alsoshown below.

[0073] {circle over (1)} Ca-α-sialon(Ca_(0.75)Si_(9.75)Al_(2.25)N_(15.25)O_(0.75)) Silicon nitride (Si₃N₄):aluminum nitride (AlN):calcium oxide (CaO)=13:9:3

[0074] {circle over (2)} Eu-α-sialon(Eu_(0.5)Si_(9.75)Al_(2.25)N_(15.25)O_(0.75)) Silicon nitride (Si₃N₄):aluminum nitride (AlN) europium oxide (Eu₂O₃)=13:9:1

[0075] {circle over (3)} Pr-α-sialon(Pr_(0.5)Si_(9.76)Al_(2.25)N_(15.25)O_(0.75)) Silicon nitride (Si₃N₄):aluminum nitride (AlN):praseodium oxide (Pr₆O₁₁)=30:27:1

[0076] {circle over (4)} Tb-α-sialon(Tb_(0.5)Si_(9.75)Al_(2.25)N_(15.25)O_(0.75)) Silicon nitride (Si₃N₄):aluminum nitride (AlN) :terbium oxide (Tb₄O₇)=26:18:1

[0077] {circle over (5)} Dy-α-sialon(Dy_(0.5)Si_(9.75)Al_(2.25)N_(15.25)O_(0.75)) Silicon nitride (Si₃N₄):aluminum nitride (AlN) :dysprosium oxide (Dy₂O₃)=13:9:1

[0078] {circle over (6)} Y-α-sialon(Y_(0.5)Si_(9.75)Al_(2.25)N_(15.25)O_(0.75)) Silicon nitride (Si₃N₄):aluminum nitride (AlN) :dysprosium oxide (Dy₂O₃)=13:9:1

[0079] {circle over (7)} Yb-α-sialon(Yb_(0.5)Si_(9.75)Al_(2.25)N_(5.25)O_(0.75)) Silicon nitride (Si₃N₄):aluminum nitride (AlN): ytterbium oxide (Yb₂O₃)=13:9:1

[0080] {circle over (8)} Er-α-sialon(Er_(0.5)Si_(9.75)Al_(2.25)N_(15.25)O_(0.75)) Silicon nitride (Si₃N₄):aluminum nitride (AlN) :erbium oxide (Er₂O₃)=13:9:1

EXAMPLE 1

[0081] Using the above material powders {circle over (1)} and {circleover (2)}, seven types of Ca-α-sialon phosphors were prepared in whichthe activating amount of Eu²⁺ ions was varied. The preparationconditions were such that the material powders were mixed in thefollowing molar ratio and reacted for one hour in a nitrogen atmosphereof 1 atm at 1,700° C. under a pressure of 20 MPa by means of a hot pressapparatus.

[0082] (1) Ca(0% Eu)-α-sialon phosphor(Ca_(0.75)Si_(9.75)Al_(2.25)N_(15.25)O_(0.75))

[0083] {circle over (1)} Ca-α-sialon alone.

[0084] (2) Ca(5% Eu)-α-sialon phosphor(Ca_(0.71)Eu_(0.025)Si_(9.75)Al_(2.25)N_(15.25)O_(0.75))

[0085] {circle over (1)} Ca-α-sialon: {circle over (2)} Eu-α-sialon=95:5

[0086] (3) Ca(10% Eu)-α-sialon phosphor(Ca_(0.68)Eu_(0.05)Si_(9.75)Al_(2.25)N_(15.25)O_(0.75))

[0087] {circle over (1)} Ca-α-sialon: {circle over (2)}Eu-α-sialon=90:10

[0088] (4) Ca(20% Eu)-α-sialon phosphor(Ca_(0.60)Eu_(0.10)Si_(9.75)Al_(2.25)N_(5.25)O_(0.75))

[0089] {circle over (1)} Ca-α-sialon: {circle over (2)}Eu-α-sialon=80:20

[0090] (5) Ca(30% Eu)-α-sialon phosphor(Ca_(0.53)Eu_(0.15)Si_(9.75)Al_(2.25)N_(16.25)O_(0.75))

[0091] {circle over (1)} Ca-α-sialon: {circle over (2)}Eu-α-sialon=70:30

[0092] (6) Ca(50% Eu)-α-sialon phosphor(Ca_(0.38)Eu_(0.25)Si_(9.75)Al_(2.25)N_(15.25)O_(0.75))

[0093] {circle over (1)} Ca-α-sialon: {circle over (2)}Eu-α-sialon=50:50

[0094] (7) Ca(70% Eu)-α-sialon phosphor(Ca_(0.23)Eu_(0.35)Si_(9.75)Al_(2.25)N_(15.25)O_(0.75))

[0095] {circle over (1)} Ca-α-sialon: {circle over (2)}Eu-α-sialon=30:70

[0096]FIG. 1 is a chart showing spectra relating to red emission ofthese phosphors (1) to (7).

[0097] In the excitation spectrum of each phosphor, broad peaks areobserved at 280 nm and at 400 to 450 nm. These two peaks show anincrease of the peak intensity with an increase of the activating amountuntil the proportion of Eu²⁺ ions doped, reaches 50%. If the activatingamount exceeds 50%, a decrease in the peak intensity occurs due tooptical loss by concentration, but even then, the peak intensity isstill higher than when the activating amount is 30%.

[0098] Of the two peaks observed in the excitation spectrum, the peak at280 nm belongs to a peak attributable to the excitation of Ca-α-sialonas the matrix material, and the peak at 400 to 450 nm belongs to thecharge transfer absorption band of Eu-(N or O). The latter peak shiftstowards a long wavelength side as the activating amount of Eu²⁺ ionsincreases, and such is useful as an excitation light (450 to 550 nm) ofInGaN type blue LED.

[0099]FIG. 2 is a chart showing emission spectra of Ca-α sialonphosphors in which the amount of Eu²⁺ ions was varied.

[0100] The observed peak was only one, and this peak shiftedcontinuously from 560 nm to 590 nm with an increase of the amount ofEu²⁺ ions. Also in such emission spectra, like the excitation spectrashown in FIG. 1, the maximum intensity of the peak was observed when theactivating amount of Eu²⁺ ions was 50%, and if the amount exceeds 50%, adecrease in the peak intensity occurred due to optical loss byconcentration, but even then, the peak intensity was still higher thanwhen the activating amount was 30%.

[0101] As mentioned above, the above Ca-α-sialon phosphors have suchEu²⁺ ion activating amounts, as the distances among Eu²⁺ ions doped areapart by about 5 Å from one another.

EXAMPLE 2

[0102] Material powders were mixed in a molar ratio of {circle over (1)}Ca-α-sialon: {circle over (2)} Pr-α-sialon=50:50. This mixed powder wasreacted for one hour in a nitrogen atmosphere of 1 atm at 1,700° C.under a pressure of 20 MPa by means of a hot press apparatus to obtain aCa-α-sialon phosphor activated by Pr³⁺ ions(Ca_(0.38)Pr_(0.25)Si_(9.75)Al_(2.25)N_(15.25)O_(0.75))

[0103] FIGS. 3(a) and 3(b) are charts showing the excitation spectrumand the emission spectrum, respectively, of the Ca-α-sialon phosphoractivated by Pr³⁺ ions.

[0104] In the excitation spectrum, a broad peak was observed at 263 nm,and a brightline peak attributable to the f-f transition of Pr³⁺ ionswas observed in the vicinity of 460 nm. In the emission spectrum,brightline peaks attributable to the f-f transition of Pr³⁺ ions wereobserved from 450 to 750 nm.

EXAMPLE 3

[0105] Material powders were mixed in a molar ratio of {circle over (1)}Ca-α-sialon: {circle over (4)} Tb-α-sialon=50:50. This mixed powder wasreacted for one hour in a nitrogen atmosphere of 1 atm at 1,700° C.under a pressure of 20 MPa by means of a hot press apparatus to obtain aCa-α-sialon phosphor activated by Tb³+ ions(Ca_(0.38)Tb_(0.25)Si_(9.75)Al_(2.25)N_(15.26)O_(0.75))

[0106] FIGS. 4(a) and 4(b) are charts showing the excitation spectrumand the emission spectrum, respectively, of the Ca-α-sialon phosphoractivated by Tb³⁺ ions.

[0107] In the excitation spectrum, a broad peak was observed at 263 nm.In the emission spectrum, brightline peaks attributable to the f-ftransition of Tb³⁺ ions were observed from 470 to 650 nm. Suchbrightline peaks were observed as a green light emission, with themaximum at 550 nm.

EXAMPLE 4

[0108] Material powders were mixed in a molar ratio of {circle over (1)}Ca-α-sialon: {circle over (2)} Eu-α-sialon: {circle over (5)}Dy-α-sialon=50:40:10. This mixed powder was reacted for one hour in anitrogen atmosphere of 1 atm at 1,700° C. under a pressure of 20 MPa bymeans of a hot press apparatus to obtain a phosphor(Ca_(0.38)Eu_(0.20)Dy_(0.05)Si_(9.75)Al_(2.25)N_(15.25)O_(0.75)) havingthe Ca-α-sialon phosphor activated by Eu³⁺ ions, further co-activated byDy³⁺ ions.

[0109] FIGS. 5(a) and 5(b) are charts showing the excitation spectrumand the emission spectrum, respectively, of the Ca-α-sialon phosphorco-activated by Eu³⁺ ions and Dy³⁺ ions.

[0110] In the excitation spectrum, two broad peaks were observed at 290nm and 450 nm. Of the two peaks, the peak at 290 nm belongs to a peakattributable to the excitation of Ca-α-sialon as the matrix material,and the peak at 450 nm belongs to the charge transfer absorption band ofEu-(N, O). The peak observed in the emission spectrum is only one, andthis peak is attributable to the d-f transition of Eu²⁺ ions.

EXAMPLE 5

[0111] Material powders were mixed in a molar ratio of {circle over (6)}Yα-sialon: {circle over (2)} Eu-α-sialon=95:5. This mixed powder wasreacted for one hour in a nitrogen atmosphere of 1 atm at 1,700° C.under a pressure of 20 MPa by means of a hot press apparatus to obtain aY-α-sialon phosphor activated by Eu³⁺ ions(Y_(0.38)Eu_(0.02)Si_(9.75)Al_(2.25)N_(15.25)O_(0.75))

[0112] FIGS. 6(a) and 6(b) are charts showing the excitation spectrumand the emission spectrum, respectively, of the Y-α-sialon phosphoractivated by Eu²⁺ ions.

[0113] In the excitation spectrum, two broad peaks were observed at 310nm and 410 nm. In the emission spectrum, a peak was observed at 570 nm,and this peak is attributable to the d-f transition of Eu²⁺ ions.

EXAMPLE 6

[0114] The above {circle over (7)} Yb²⁺ α-sialon(Yb_(0.5)Si_(9.75)Al_(2.25)N_(15.25)O_(0.75)) was used by itself as aphosphor.

[0115] In FIG. 7, (a) and (b) are charts showing the excitation spectrumand the emission spectrum, respectively, of the Yb²⁺ α-sialon phosphor.

[0116] In the excitation spectrum, a broad peak was observed at about240 nm. In the emission spectrum, a peak was observed at 510 nm, andthis peak is attributable to the d-f transition of Yb²⁺ ions.

EXAMPLE 7

[0117] The above {circle over (8)} Eu-α-sialon(Er_(0.5)Si_(9.75)Al_(2.25)N_(15.25)O_(0.75)) was used by itself as aphosphor.

[0118] In FIG. 8, (a) and (b) are charts showing the excitation spectrumand the emission spectrum, respectively, of the Er³⁺ α-sialon phosphor.

[0119] In the excitation spectrum, a broad peak was observed at 263 nm,and brightline peaks attributable to the f-f transition of Er³⁺ ionswere observed in the vicinity of 400 nm. In the emission spectrum,brightline peaks attributable to the f-f transition of Er³⁺ ions wereobserved from 500 to 600 nm.

[0120] Now, the second aspect of the present invention will be describedin further detail with reference to Examples.

EXAMPLE 8

[0121] A mixture of Si₃N₄:Eu₂O₃:CaO:AlN=79.0:1.5:2.2:15.8 (molar ratio)(provided that CaO was added in the form of calcium carbonate) wascompacted under a pressure of 200 kg/cm² by a mold having a diameter of10 mm and then subjected to hot press sintering under a pressure of 20MPa for one hour at 1,750° C. in a nitrogen atmosphere. After theheating, the sintered product was pulverized, and the powder X-raydiffraction was measured, whereby a material comprising 66 wt % ofα-sialon, 18 wt % of β-sialon and 15 wt % of unreacted a-siliconnitride, was obtained.

[0122] If the composition of the powder as a whole is represented by acomposition formula of α-sialon, it will be (Ca_(0.11)Eu_(0.14)) (Si,Al)₁₂(O, N)₁₆. The excitation spectrum of the material is shown by solidline 1 in FIG. 10, wherein the peak at about 300 nm is attributable toexcitation of the Ca-α-sialon as the matrix material, and the peak at350 to 500 nm belongs to the charge transfer absorption band of Eu-(O,N), which indicates that InGaN type blue LED (450 to 500 nm) can be usedas an excitation light. The emission spectrum is shown by solid line 1in FIG. 11 and has a peak in the vicinity of 580 nm.

EXAMPLE 9

[0123] A mixture of Si₃N₄:Eu₂O₃:CaO:AlN:Al₂O₃=75.9:1.0:3.2:17.2:1.72(molar ratio) (provided that CaO was added in the form of calciumcarbonate) was compacted under a pressure of 200 kg/cm² by a mold havinga diameter of 10 mm and then heated for two hours at 1,750° C. in anargon atmosphere. After the heating, the sintered product waspulverized, and the powder X-ray diffraction was measured, whereby amaterial comprising 68 wt % of α-sialon, 24 wt % of β-sialon and 8 wt %of unreacted a-silicon nitride, was obtained. If the composition of thepowder as a whole is represented by a composition formula of α-sialon,it will be (Ca_(0.15), Eu_(0.06)) (Si, Al)₁₂ (O, N)₁₅. The materialshowed an excitation peak at 350 to 500 nm and an emission peak at 550to 650 nm, as shown by dotted line 2 in FIG. 10 and dotted line 2 inFIG. 11, respectively.

EXAMPLE 10

[0124] A mixture of Si₃N₄:Tb₂O₃:CaO:AlN=79.0:1.5:2.2:15.8 (molar ratio)(provided that CaO was added in the form of calcium carbonate) wascompacted under a pressure of 200 kg/cm² by a mold having a diameter of10 mm and then heated for two hours at 1,700° C. in a nitrogenatmosphere. After the heating, the sintered product was pulverized, andthe powder X-ray diffraction was measured, whereby a material comprising68 wt % of α-sialon, 16 wt % of β-sialon and 16 wt % of unreactedα-silicon nitride, was obtained. If the composition of the powder as awhole is represented by a composition formula of α-sialon, it will be(Ca_(0.11), Tb_(0.14)) (Si, Al)₁₂ (O, N)₁₆. The material showed a lightemission having main peaks at about 400 nm and 540 nm.

EXAMPLE 11

[0125] A mixture of Si₃N₄:Yb₂O₃:CaO:AlN:Al₂O₃=75.9:1.0:3.2:17.2:1.72(molar ratio) (provided that CaO was added in the form of calciumcarbonate) was compacted under a pressure of 200 kg/cm² by a mold havinga diameter of 10 mm and then heated for two hours at 1,750° C. in anitrogen atmosphere. After the heating, the sintered product waspulverized, and the powder X-ray diffraction was measured, whereby amaterial comprising 70 wt % of α-sialon, 22 wt % of β-sialon and 8 wt %of unreacted α-silicon nitride, was obtained. If the composition of thepowder as a whole is represented by a composition formula of α-sialon,it will be (Ca_(0.15), Yb_(0.06)) (Si, Al)₁₂ (O, N)₁₆. The materialshowed a light emission having a broad peak at 450 to 600 nm.

[0126] The present invention is by no means restricted by theabove-mentioned embodiments or Examples. With respect to details ofpreparation of materials, the molar ratios and the productionconditions, various changes or modifications are, of course, possible.

[0127] As described in detail in the foregoing, with the oxynitridephosphor activated by a rare earth element, of the present invention,the position of its excitation spectrum shifts towards a long wavelengthside as compared with conventional oxide phosphors, and the absorptionpeak overlaps the luminescence (459 to 500 nm) emitted by blue LED.Thus, the present invention provides the oxynitride phosphor activatedby a rare earth element, which makes high luminance of white LEDpossible by using blue LED as a light source.

[0128] Further, the oxynitride phosphor activated by a rare earthelement of the present invention is excellent in thermal and mechanicalproperties and further in the chemical stability, since the matrixmaterial is α-sialon. Accordingly, the present invention provides theoxynitride phosphor activated by a rare earth element, which is capableof being operated stably even in a severe environment, i.e. which isexcellent in life time.

[0129] Likewise, the α-sialon type phosphor of the present inventionshifts the excitation spectrum towards a long wavelength side ascompared with the conventional oxide phosphors, and the absorption peakoverlaps the luminance (450 to 500 nm) of blue LED. Thus, the presentinvention provides a phosphor which makes high luminance of white LEDpossible by using blue LED as an excitation light source.

[0130] Further, α-sialon has been developed as a heat resistancematerial and thus has thermal, mechanical and chemical stability. Thus,the present invention provides an α-sialon type phosphor which can beoperated stably even in a severe environment and which is excellent inlife time.

[0131] The entire disclosures of Japanese Patent Application No.2001-171831 filed on Jun. 7, 2001 and Japanese Patent Application No.2002-149022 filed on May 23, 2002 including specifications, claims,drawings and summaries are incorporated herein by reference in theirentireties.

What is claimed is:
 1. An oxynitride phosphor activated by a rare earthelement, represented by the formulaMe_(x)Si_(12−(m+n))Al(m+n)O_(n)N_(16−n):Re1_(y)Re2_(x), wherein a partor all of metal Me (where Me is at least one metal selected from thegroup consisting of Ca, Mg, Y and lanthanide metals excluding La and Ce)in α-sialon solid solution, is substituted by lanthanide metal Re1(where Re1 is at least one metal selected from the group consisting ofCe, Pr, Eu, Tb, Yb and Er), or two lanthanide metals Re1 and acoactivator Re2 (where Re2 is Dy), to be an emission center.
 2. Theoxynitride phosphor activated by a rare earth element according to claim1, wherein when metal Me is bivalent, 0.6<m<3.0 and 0≦n<1.5.
 3. Theoxynitride phosphor activated by a rare earth element according to claim1, wherein when metal Me is trivalent, 0.9<m<4.5 and 0≦n<1.5.
 4. Theoxynitride phosphor activated by a rare earth element according to claim1, wherein m=1.5, n=0.75 and in the composition formulaMe_(x)Si_(9.75)Al_(2.25)O_(0.75)N_(15.25):Re1_(y)Re2_(z), 0.3<x+y<0.75and 0.01<y+z<0.7 (where y>0.01 and 0.0≦z<0.1).
 5. The oxynitridephosphor activated by a rare earth element according to claim 4, wherein0.3<x+y+z<1.5, 0.01<y<0.7 and 0≦z<0.1.
 6. The oxynitride phosphoractivated by a rare earth element according to claim 2, wherein metal Meis Ca.
 7. A sialon type phosphor in the form of a powder comprising atleast 40 wt % of α-sialon represented by the formula (Ca_(x), M_(y))(Si, Al)₁₂ (O, N)₁₆ (where M is at least one metal selected from thegroup consisting of Eu, Tb, Yb and Er, 0.05<(x+y)<0.3, 0.02<x<0.27 and0.03<y<0.3) and having a structure such that Ca sites of Ca-α-sialon arepartially substituted by other metal M, at most 40 wt % of β-sialon, andat most 30 wt % of unreacted silicon nitride.
 8. The sialon typephosphor according to claim 7, wherein the chemical composition of thepowder as a whole, is within a range defined by three compositionallines of Si₃N₄−a(M₂O₃˜9AlN), Si₃N₄−b(CaO·3AlN) and Si₃N₄−c(AlN·Al₂O₃),where 4×10⁻³<a<4×10⁻², 8×10⁻³<b<8×10⁻² and 10 ⁻²<c<10⁻¹.